DAC with ocean storage

From $812/tonne

Overview

This process uses seawater electrolysis to capture and convert atmospheric CO₂ into two forms: carbonate solids (which can be used in construction) and dissolved bicarbonate ions that are permanently stored in the ocean.

Our supplier’s approach is unique because it does this onshore in a closed system, making it easier to measure carbon removal.

Using electrolysis, water is split into two streams. One stream is acidic, and the other is alkaline. The alkalinity leads to the formation of solid calcium carbonate and magnesium hydroxide. The calcium carbonate formation removes CO₂ from the water and forms solids (limestone) that can be stored or used in construction. In the second step, the alkaline stream containing the magnesium hydroxide solids is contacted with air, which converts atmospheric CO₂ into bicarbonate ions.

The electrolysis process strips the seawater of its magnesium and calcium ions. In order to maintain the original chemistry before the water is re-released into the ocean, the cations are replenished. This is done by running the acidic stream over silicate rocks, which releases magnesium and calcium ions back into the water. Then the two streams are combined again under rigorous monitoring to ensure the water leaving the plant has a similar composition to that that came in, and is compliant with permitting regulations.

The science

Vast availability of Ca²⁺ and Mg²⁺ ions in the oceans means that CO₂ dissolved in seawater should be able to readily precipitate into Mg-carbonates and Ca-carbonates. However, kinetic constraints mean this is largely prohibited. Certain organisms have evolved to overcome these constraints using biological processes.

For example, to produce calcium carbonate shells. However, abiotic precipitation is very rare. In Equatic’s process, electrolysis is used to create high pH conditions in order to overcome these constraints. This leads to the instantaneous precipitation of calcium carbonate (CaCO₃) and magnesium hydroxide (Mg(OH)₂).

The CaCO₃ precipitation represents the removal and highly permanent storage of CO₂ previously dissolved in seawater. However, the majority of the CDR in this process comes from a second stage in which the alkaline stream containing the precipitated Mg(OH)₂ and remaining Ca²⁺ ions is aerated. This aeration process leads to the absorption of CO₂ which causes the progressive dissolution of Mg(OH)₂. The result is the immobilization of this atmospherically derived CO₂ in the form of bicarbonate ions (HCO₃⁻) and further CaCO₃ precipitation.

Dissolved oceanic CO₂ concentrations are highly dependent on the pH of the water. This is what helps the absorption of CO₂ by the alkaline stream during the aeration process. However, it also highlights the importance of neutralising the acidic stream. Silicate rocks are used to both neutralise this acidic stream and reintroduce Ca²⁺ and Mg²⁺ ions to the water prior to the effluent being released to the ocean. This ensures no pH related degassing will occur and no major changes to ocean chemistry occur during the process.

Both the bicarbonate and calcium carbonate production immobilizes CO₂ for over 10,000 years. There is an incredibly low risk of reversal making this one of the most permanent methods of CDR available.

Research papers 3

Supercritical‘s view

The ocean is the world’s largest natural carbon sink and oceanic carbon sequestration is pivotal for large-scale CDR.

We love this project because it is a scalable, oceanic initiative with a robust measurement, reporting and verification (MRV) blueprint. While similar to conventional DAC and ocean-alkalinity enhancement, it offers a unique approach to CDR.

By operating in a closed system, all of the inputs, outputs and processes can be monitored as they happen. The co-production of green hydrogen only adds to this great project by offering an alternative way of reducing the energy requirements of the project.

Dr Mai Bui

Director of climate science

Our suppliers

Spun out of UCLA’s institute for Carbon Management, Equatic is a really exciting company with grand ambitions for gigatonne scale carbon removal.

With two sites operating, a data-led approach and a great team our partnership allows us to support a company that is helping to scale carbon removal with integrity and credibility.

California, USA
Singapore

Verifications

Every project in the marketplace receives a score through our science-driven, commercially-focused vetting protocol.

Covering 100+ criteria across four key dimensions, this rigorous evaluation yields top-line scores, allowing you to compare projects and evaluate quality objectively. Dive deeper with our vetting explainer.

Climate science

Is the climate science that underpins the carbon credit rock solid?
- Remove carbon
- Have clear permanence
- Accurately issue credits
- Is additional
- Does not suffer leakage
- Strong MRV (Measured, Reported and Verified)
Environmental factors

Beyond the removal of CO2, does the project have a positive or negative impact on the local environment?
- Neutral or positive impact on biodiversity
- Neutral or positive impact on air quality
- Neutral or positive impact on soil health
- No negative effects on groundwater
Delivery risk

What is the risk of non-delivery of credits?
- Site development
- Site operational track record
- Team experience and capability
- Business plan and funding
- Levels of geopolitical risk
Social impact

Does the project have a positive or negative impact on local communities, per UN Sustainable Development Goals (SDGs)?
- Economic empowerment of local communities
- Integrates education and community engagement
- Better health outcomes

Browse our removal methods

Biochar

Biochar is charcoal-like material rich in stable carbon. It is produced by heating biomass in an oxygen-limited environment in a process called pyrolysis.

Permanence: MEDIUM From: $162/t
ARR

Afforestation and forest restoration, if done effectively, combat climate change by removing carbon dioxide and protecting biodiversity.

Permanence: LOW From: $58/t
Enhanced weathering

Enhanced rock weathering (ERW) takes natural weathering of silicate rocks that removes & mineralizes atmospheric CO₂ and speeds it up dramatically.

Permanence: HIGH From: $312/t
Direct air capture

Direct air capture (DAC) is a chemical process to capture ambient CO₂ from the atmosphere.

Permanence: HIGH From: $618/t
DAC with ocean storage

This employs seawater electrolysis to capture and convert atmospheric CO₂ into carbonate solids for construction and permanently stores dissolved bicarbonate ions in the ocean.

Permanence: HIGH From: $812/t
Woody biomass sinking

This is a method that sequesters carbon by submerging leftover woody materials in the oxygen-depleted layer of the Black Sea, which is approximately 2 kilometers deep.

Permanence: MEDIUM From: $375/t
Bio-oil

Bio-oil and biochar production both convert waste biomass through pyrolysis. Bio-oil is a liquid stored in geological repositories, while biochar is applied to soils.

Permanence: HIGH From: $750/t